Traditionally, expensive test equipment has been required to dynamically monitor the functional interactions of integrated circuits on a circuit board design. During test, the integrated circuits are made to operate together functionally while an external tester observes the transactions occurring between the integrated circuits. Other techniques such as boundary scan provide off-line or static testing of wiring interconnects between integrated circuits, but are not effective in detecting at-speed functional problems that can occur in the bussing paths between integrated circuits.
The ability to dynamically (i.e., during normal operation of the circuit board) observe the data passing between integrated circuits in real-time allows monitoring of the functional interactions between multiple integrated circuits on a substrate, such as a circuit board. Such a test can reveal timing sensitive and/or intermittent failures that would otherwise not be detectable without the use of expensive testers and mechanical probing fixtures. The ability to dynamically observe system data buses in real-time facilitates system integration, environmental chamber testing, remote diagnostic testing, and built-in self testing.
Heretofore, the ability to dynamically observe digital signals on buses formed of leads on the substrate or circuit board between integrated circuits has been unavailable. Current test methods used to monitor or observe digital signals on signal paths or leads between integrated circuits on substrate or circuit board designs require the use of expensive external tester equipment and signal node probing mechanisms. One problem with the current test approach is that state-of-the-art circuit board designs are so densely populated with integrated circuits that physical probing of the signal paths is very difficult, if not impossible. Another problem is that the circuit board tester is dependent upon the availability of external testers and probing fixtures. Transportation and upkeep of the required test equipment in a field environment to support a system can be a very expensive proposition.
Therefore, a need has arisen to provide a digital bus monitoring device which can be used to dynamically observe data or address signals on bus leads connecting multiple integrated circuits.